I have been wondering for the past while, in the eyes of a non “Incel”, but from someone who knows them, why are these people undatable?

The reason is that the female's assessment of male attractiveness is different from the males assessment.

If you give a group of men a series of images of women and ask them to rate attractiveness as "above average", "average" or "below average" you will get a classic "bell curve" with 50% of women above and 50% below the average. But if you ask a group of women to rate pictures of men the bell-curve is skewed with only 20% above average and 80% below average.

This means that the less physically attractive males don't stand a chance. They would probably be quite happy to date a less attractive woman, but these women are chasing average looking guys, while the average looking women are chasing the better-looking guys.

Incels are nearly all male and it's virtually impossible for a woman to genuinely be an incel. If a woman complains she can't get a date it means she can't find someone good enough to date, and the men who are showing an interest are the ones she thinks are beneath her. Whereas when a man can't get a date it means he literally has no chance at all of getting a date.

It's complete nonsense to say that incel guys have "unrealistic standards". Incel guys would date any woman, but even unattractive women turn them down.

They aren't "undateable", they just have unrealistic standards for whom they're willing to date.